alarge-scalesynthesisandcharacterizationof quaternarycuin...

Hindawi Publishing CorporationInternational Journal of Chemical EngineeringVolume 2011, Article ID 545234, 8 pagesdoi:10.1155/2011/545234

Research Article

A Large-Scale Synthesis and Characterization ofQuaternary CuInxGa1−xS2 Chalcopyrite Nanoparticles viaMicrowave Batch Reactions

Chivin Sun,1 Richard D. Westover,1 Gary Long,1 Cyril Bajracharya,1 Jerry D. Harris,2

Alex Punnoose,3 Rene G. Rodriguez,1 and Joshua J. Pak1

1 Department of Chemistry, Idaho State University, Pocatello, ID 83209, USA2 Department of Chemistry, Northwest Nazarene University, Nampa, ID 83686, USA3 Department of Physics, Boise State University, Boise, ID 83725, USA

Correspondence should be addressed to Joshua J. Pak, [email protected]

Received 29 March 2011; Accepted 9 August 2011

Academic Editor: Deepak Kunzru

Copyright © 2011 Chivin Sun et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Various quaternary CuInxGa1−xS2 (0 ≤ x ≤ 1) chalcopyrite nanoparticles have been prepared from molecular single-sourceprecursors via microwave decomposition. We were able to control the nanoparticle size, phase, stoichiometry, and solubility.Depending on the choice of surface modifiers used, we were able to tune the solubility of the resulting nanoparticles. Thismethod has been used to generate up to 5 g of nanoparticles and up to 150 g from multiple batch reactions with excellentreproducibility. Data from UV-Vis, photoluminescence, X-ray diffraction, TEM, DSC/TGA-MS, and ICP-OES analyses have shownhigh reproducibility in nanoparticle size, composition, and bandgap.

1. Introduction

For nearly three decades, chalcopyrite CuIn0.7Ga0.3Se2

(CIGS) and related materials have attracted much interestdue to their potential applications in photovoltaic and otheroptoelectric devices [1–5]. Many thin film PV devices ofCIGS set respectable power conversion efficiency of about20% [6, 7]. In recent years, there have been increasing reportson using colloidal I–III–VI nanoparticle suspensions, com-posites, and inks to prepare PV devices. Solution processingstrategies such as spin coating [8–10] and ink printing [1, 2,4] are being explored for large areas of CIGS while loweringthe overall costs.

One of the key stoichiometric requirements is to consis-tently maintain In/Ga ratio to 0.7/0.3 from batch to batch.Previously, we reported the efficient syntheses of quaternaryCuInxGa1−xS2 (0 ≤ x ≤ 1) chalcopyrite nanoparticleswith precise stoichiometric control by decomposition ofa mixture of two I–III bimetallic single-source precursors

(SSPs), (Ph3P)2Cu(μ-SEt)2In(SEt)2 (1), and (Ph3P)2Cu(μ-SEt)2Ga(SEt)2 (2), in the presence of 1,2-ethanedithiol viamicrowave irradiation [11].

Use of SSPs in preparation of nanomaterials presentsdistinct advantages such as precise control of reaction con-ditions and stoichiometry as SSPs contain all necessary ele-ments in a single molecule. Despite the obvious advantagesof SSPs, to our knowledge, no studies have been conductedusing combinations of SSPs to form soluble and insolubleternary and quaternary chalcopyrite nanoparticles.

Microwave-assisted preparation of nanoparticles fromSSPs offers advantages over traditional thermolysis as micro-wave provides rapid heating as well as greater homogeneity inthe overall reaction temperature [12]. This usually allows forthe preparation of nanoparticles with increased size control[13], dramatic decreases in reaction times, improved productpurities, and reactions exhibiting good reproducibility andhigh yields [14, 15].

2 International Journal of Chemical Engineering

In our studies, the nanoparticles were produced using1,2-ethanedithiol as surface stabilizer and cross-linker ofSSPs. 1,2-Ethanedithiol undergoes thiolate ligand exchangereactions, which produce random copolymers of SSPs. Thisformation of random copolymers between SSPs 1 and3 is a important requirement for us to control In-Garatio in nanoparticles. 1,2-Ethanedithiol also cross-links na-noparticles, and the resulting organic-nanoparticle compos-ite precipitates out of reaction solution as insoluble micron-sized clusters [14]. Although the resulting material exhibitedexcellent size, stoichiometry, and bandgap control, thesemicron-sized clusters are not suitable for some solution-based thin film processing methods, which require highlysoluble nanoparticles in common organic solvents. There-fore, the ability to modulate organic constituents on theseCIGS nanoparticles whether to improve solubility or toadd functionality through a hybrid composite is important.Judicious use of organic cross-linking agents in conjunctionwith other monothiols can control the solubility of resultingnanoparticles. The ability to modulate both physical andchemical properties could lead to future applications of theseparticles in organic-inorganic composites in photovoltaics[16–19], biological investigations [20, 21], and catalysis [22].

The full realization of the potential of these nanoparticleswill require synthetic strategies capable of consistently pro-ducing nanoparticles on a multigram scale. Despite the ob-vious needs, scales of tens of milligrams are typical for theproduction of CIS and CIGS nanoparticles [23–26]. Thusfar, the production of these nanoparticles on a gram scaleor larger has received limited attention [11, 14, 27–29]. Inaddition, the preparation of soluble CuInxGa1−xS2 nanopar-ticles with precise stoichiometric control has not been re-ported to best of our knowledge on any scale.

We recently discovered that the reaction of two SSPs withlimited amount of 1,2-ethanedithiol as a cross-linker and ex-cess of 1-hexanethiol as a surface modifier provides a wayto tune the solubility from insoluble to soluble nanoparticleswhile maintaining precise stoichiometric control.

Herein, we report the preparation of quaternaryCuInxGa1−xS2 (0 ≤ x ≤ 1) chalcopyrite nanoparticles withtunable bandgap and solubility on scales of up to 150 g withprecise stoichiometric control by selectively decomposingmixtures of SSPs 1 and 2 or mixtures of SSPs 3 and 4(Figure 1) via microwave irradiation.

2. Experimental

2.1. General Considerations. Triphenylphosphine (Ph3P,99+%), 1,2-ethaneditiol (HSCH2CH2SH, 99.8%), benzylacetate (C6H5CH2CO2CH3, 99%), gallium (III) chloride(GaCl3, ultradry, 99.999%, metals basis), and indium (III)chloride (InCl3, anhydrous 99.99%, metals basis) were pur-chased from Alfa Aesar. Ethanethiol (CH3CH2SH, 99+ %),1-hexanethiol (CH3(CH2)5SH, 96%), thiophenol (PhSH,99+%), and copper (I) chloride (CuCl, 99.999%, extra pure,purified) were purchased from Acros Organics. All other sol-vents (benzene, tetrahydrofuran, diethyl ether, and pentane)were dried and degassed using an Innovative Technology

Inc. solvent purification system (activated alumina, coppercatalyst, and molecular sieves columns) before use. All otherreagents were obtained from commercial sources and usedwithout further purification. Milestone microwave (Lab-station ETHOS EX) was used with a 15 min ramp and a 45or 60 min hold at desired reaction temperatures. The re-sulting nanoparticles were characterized using a JEOL 2010high-resolution transmission electron microscope (HRTEM)with a spatial resolution of 0.194 nm. Powder X-ray dif-fraction (XRD) patterns were acquired with a Bruker D8Discover diffractometer using CuKa radiation source and ascintillation detector. Scans were collected for 4 hrs em-ploying a 0.06◦ step width at a rate of 10 s/step resultingin a 2θ scanning range from 10 to 60◦. Absorption spectraof nanoparticles were obtained from UV-Vis data re-corded on a Shimadzu UV-Vis scanning (UV-3101PC)spectrophotometer using an integrating sphere moduleat room temperature. Inductively, coupled plasma-opticalemission spectroscopy (ICP-OES) analysis was accomplishedby weighing 20 mg of each nanoparticle sample thendigesting in concentrated HNO3 to make a 10 ppm solution.All samples were run within 24 hours of preparing thesolution to ensure that the results were consistent. All ICPdata were recorded on a Varian 715-ES (ICP-OES withV-groove Nebulizer). Photoluminescence spectra wererecorded using a Horiba Jobin Yvon Fluoromax-3 spec-trofluorometer with 1 cm path length cells. The cells werecleaned, and samples were prepared with spectroscopic-grade benzene. The thermal degradation of the nanoparticleswas characterized using a Mettler Toledo TGA/DSC1 thermalanalyzer, connected to a Pfeiffer Vacuum ThermoStar massspectrometer. Thermal characterization was preformed in anargon environment, with ramp rates of 10–50◦C/min from50◦C to 600◦C in alumina crucibles.

2.2. Synthesis of Single-Source Precursors (SSPs) [30–33].(Ph3P)2Cu(μ-SEt)2In(SEt)2 (1), (Ph3P)2Cu(μ-SEt)2Ga(SEt)2

(2), (Ph3P)2Cu(μ-SPh)2In(SPh)2 (3), and (Ph3P)2Cu(μ-SPh)2Ga(SPh)2 (4) were synthesized according to the liter-ature [30–33].

2.3. General Procedure for the Preparation of CuInxGa1−xS2

(0 ≤ x ≤ 1) Chalcopyrite Nanoparticles [11]. For the generalreaction, in a dry Milestone microwave vessel, (Ph3P)2Cu(μ-SEt)2In(SEt)2 (SSP 1, 1.500 g, 1.583 mmoL) and (Ph3P)2

Cu(μ-SEt)2Ga(SEt)2 (SSP 2, 1.429 g, 1.583 mmoL) were dis-solved in 18 mL of dry benzyl acetate followed by addi-tion of 1,2-ethanedithiol (1.8 mL, 21.46 mmoL). The re-action mixture was stirred at room temperature for 5 minand heated at set temperatures for 1 hour via microwave ir-radiation. Upon completion, the reaction was cooled toroom temperature, and CuIn0.5Ga0.5S2 nanoparticles wererecovered by serial precipitation, centrifugation, and washingin CH3OH to provide yellow to black powder.

2.4. Preparation of Highly Cross-Linked QuaternaryCuIn0.7Ga0.3S2 Chalcopyrite Nanoparticles from SSPs 3 and 4.For the general reaction, in a dry Milestone microwave vessel,(Ph3P)2Cu(μ-SPh)2In(SPh)2 (3, 13.61 g, 11.95 mmoL),

International Journal of Chemical Engineering 3

S S

SS

Cu In

Ph3P

Ph3P

Et

Et

Et

Et

S S

SS

Cu

Ph3P

Ph3P

Et

Et

Et

Et

Ga

S S

SS

Cu In

Ph3P

Ph3P

Ph

Ph

Ph

Ph

Ga

S S

SS

Cu

Ph3P

Ph3P

Ph

Ph

Ph

Ph

1 2 3 4

Figure 1: Single-source precursors 1 through 4.

(Ph3P)2Cu(μ-SPh)2Ga(SPh)2 (4, 6.43 g, 5.87 mmoL), and1,2-ethanedithiol (9.72 mL, 115.9 mmoL) were dissolvedin 88.0 mL of benzyl acetate. The reaction was heated atreaction temperatures 160, 180, or 200◦C for 1 hr. Uponcompletion, the reaction was cooled to room temperature,and CuIn0.7Ga0.3S2 nanoparticles were recovered by serialprecipitation, centrifugation, and washing with CH3OH toprovide black powder. This method has been successfullyadapted to prepare up to 5 g of nanoparticles in a singlevessel (Figure 2).

2.5. Preparation of Organic Soluble QuaternaryCuInxGa1−xS2 (0 ≤ x ≤ 1) Chalcopyrite Nanoparticles.(Ph3P)2Cu(μSEt)2In(SEt)2 (1, 6.00 grams, 6.33 millimoles)and (Ph3P)2Cu(μ-SEt)2Ga(SEt)2 (2, 5.71 grams,6.33 millimoles) were dissolved in 60 mL of benzene, and1,2-ethaneditiol (1.06 mL, 12.66 millimoles) was added toafford random polymer of 1 and 2. After stirring at roomtemperature for 1 hr, the solvent and ethanethiol wereremoved to afford white solid. The resulting solid wasredissolved in benzyl acetate (20 mL) followed by addition of1-hexanethiol (2.00 mL). The reaction was heated at reactiontemperatures between 160 and 200◦C for 1 hr. Uponcompletion, the reaction was cooled to room temperature,and CuInxGa1−xS2 (0 ≤ x ≤ 1) nanoparticles were recoveredby serial precipitation, centrifugation, and washing inCH3OH to provide red to red-black powder.

2.6. Preparation of Organic Soluble Quaternary CuIn0.7Ga0.3S2

Chalcopyrite Nanoparticles. Following general reaction, acombination of two SSPs, (Ph3P)2Cu(μ-SEt)2In(SEt)2 (SSP1, 13.00 g, 13.72 mmoL) and (Ph3P)2Cu(μ-SEt)2Ga(SEt)2

(SSP 2, 6.67 g, 7.39 mmoL), dissolved in 100 mL of ben-zyl acetate in the presence of 1,2-ethanedithiol (2.4 mL,28.50 mmoL) and 1-hexanethiol (20 mL, 142.1 mmoL). Thereaction was heated at 195◦C for 1 h. Upon completion,the reaction was cooled to room temperature, andCuIn0.7Ga0.3S2 nanoparticles were recovered by serial pre-cipitation, centrifugation, and washing in CH3OH to pro-vide red-black powder. This method has been successfullyadapted to prepare up to 25 g of nanoparticles in a singlevessel.

3. Results and Discussions

We recently reported the efficient microwave syntheses ofhighly cross-linked quaternary CuInxGa1−xS2 (0 ≤ x ≤1)chalcopyrite nanoparticles in subgram scales. The methoddemonstrated high degrees of stoichiometric controlby decomposing a mixture of two I–III bimetallicSSPs, (Ph3P)2Cu(μ-SEt)2In(SEt)2 (1) and (Ph3P)2Cu(μ-SEt)2Ga(SEt)2 (2), using 1,2-ethanedithiol as a cross-linker.The resulting nanoparticles could be engineered to exhibitbandgaps ranging from 1.59 to 2.30 eV by varying theamount of Ga in CuInxGa1−xS2 nanoparticles [11].

These highly cross-linked quaternary nanoparticles areinsoluble in common organic solvents but retain individualnanoparticle characteristics such as phase, size, and bandgap.As expected, XRD peaks associated with chalcopyrite phaseshift toward narrower lattice spacing, as a function ofincreasing amount of Ga [11].

In order to increase reproducibility of large-scale reac-tions, we chose (Ph3P)2Cu(μ-SPh)2In(SPh)2 (SSP 3) and(Ph3P)2Cu(μ-SPh)2Ga(SPh)2 (SSP 4) to be used in placeof SSPs 1 and 2. Due to their bulky and hydrophobicphenylthiolate ligands, SSPs 3 and 4 are more stabletowards moisture and thermal decomposition compared totheir ethylthiolate counterpart [33]. This allows for easierhandling and greater reproducibility in larger reactions.The CuIn0.7Ga0.3S2 nanoparticles have been synthesized (29separate reactions resulting in about 150 g of nearly uniformnanoparticles under the same reaction conditions) fromdecomposition of SSPs 3 and 4 via microwave irradiationin the presence of 1,2-ethanedithiol at 200◦C with highreproducibility.

The analysis of CuIn0.7Ga0.3S2 nanoparticles by ICP-OES(Table 1) indicates that our method allows precise controlof In/Ga ratio. The high level of control is likely due to thefact that 1,2-ethanedithiol acts as a bridging unit betweentwo SSP units. This process produces cross-linked randompolymers of SSPs, which undergo rapid decomposition toproduce the resulting CuInxGa1−xS2 nanoparticles [14]. TheICP-OES data of CuIn0.7Ga0.3S2 nanoparticles also showevidence of little or no change in the atomic percent of Cu, In,and Ga for all 29 reactions, Table 1. These results exhibit highreproducibility, improved product purities, and indicate thatdifferent forms of precursors can be used. The target formulaof CuIn0.7Ga0.3S2 was achieved by using 7 : 3 ratio of SSPs 3and 4.


=HSCH2CH2SH

=HS(CH2)5CH3

Highly cross-linked

insoluble

Soluble

or

HS

HS

SH

S S

SS

Cu In

Ph3P

Ph3P

Et

Et

Et

Et

S S

SS

Cu

Ph3P

Ph3P

Et

Et

Et

Et

Ga+

Figure 2: Formation of soluble and insoluble CIGS nanoparticles from SSPs by controlling the ratio between 1,2-ethanedithiol and 1-hexanethiols.

Table 1: Representative sample compositions (from ICP-OES analysis) from 10 of 29 highly cross-linked CuIn0.7Ga0.3S2 nanoparticle batchesprepared at 200◦C. ∗The standard deviation of all samples is 0.89 for Cu, 0.96 for In, and 0.35 for Ga.

EntryAtomic percent (Raw)

In+Ga In/In+Ga Ga/In+Ga[Cu]∗ [In]∗ [Ga]∗

1 19.59 12.26 5.45 17.71 0.69 0.31

2 20.77 12.41 5.38 17.80 0.70 0.30

3 21.48 14.38 6.14 20.52 0.70 0.30

4 20.17 13.14 6.29 19.43 0.68 0.32

5 20.26 14.42 5.51 19.93 0.72 0.28

6 21.67 14.96 5.92 20.88 0.72 0.28

7 20.51 13.94 5.94 19.88 0.70 0.30

8 19.90 13.23 5.89 19.12 0.69 0.31

9 19.91 13.28 5.72 19.00 0.70 0.30

10 21.79 14.75 6.20 20.96 0.70 0.30

The estimated volume-weighted crystal diameters (em-ploying Scherrer equation with a shape factor of 0.9) [34]of the CuIn0.7Ga0.3S2 chalcopyrite nanoparticles samples are4.4± 0.4 nm (Figure 3(a)). As shown in Figure 3(b), multiplebatch samples exhibit almost identical absorption behaviorwith the average bandgap of 1.55 ± 0.05 eV.

Similar method can be used to prepare quaternaryCuIn0.7Ga0.3S2 chalcopyrite nanoparticles, which are solublein common organic solvents such as hexanes, THF, andCH2Cl2. The increased solubility is attributed to the use oflimited amount of 1,2-ethanedithiol in presence of excess 1-hexanethiol in the reaction mixture. Other monothiols withlonger carbon chains and branched structures can also beused to modulate the resulting solubility.

From our previous experience, high-reaction tempera-ture and/or the use of more than 2 equiv. of cross-link-ing agent is necessary to fully incorporate Ga to the crys-talline structure. As shown in ICP-OES data (Table 2), Gaincorporation increases at higher reaction temperatureswhen 1:1 ratio of SSP 1 and 2 is used. However, the use ofincreasing amounts of 1,2-ethanedithiol leads to decreasingsolubility, and the higher reaction temperatures result inlarger particle sizes [11].

Thermogravimetric analyses (TGA/DSC-MS) of the sol-uble nanoparticles were performed at ambient pressure inalumina crucibles. The samples were heated at a rate of10◦C/min under an argon atmosphere. Weight loss was as-sociated with decomposition of the passivation layers(Figure 4). Calculation of the derivative maximum rate ofweight loss (MRW, %/◦C) and step transition weight losswere used as a measure of relative stability. The TGA datashow a smooth loss of mass over a temperature windowof 250–400◦C in two steps, accounting for a loss of 34.6%,30.1%, and 28.4% for entries 11–13 (Table 2), respectively.The evolved gases were thermal decomposition productsof 1,2-ethanedithiol and 1-hexanethiol as expected. Theseresults are consistent with the ICP-OES analysis, a decreasein particle size results in a relative increase in the amount oforganic material that makes up the passivation layer.

A bandgap range from 1.76 to 1.84 eV was obtained basedon the absorption spectra. The estimated volume-weightedcrystal diameters [34] of the CuInxGa1−xS2 chalcopyritenanoparticles samples based on the XRD spectra are from3.7 to 3.9 nm (Figure 5(a)). The photoluminescence emission(PLE) maxima increases can also be directly related to theincrease in bandgap with increased Ga content (Figure 5(b)).


2θ

Rel

ativ

ein

ten

sity

10 20 30 40 50 60

(a)

Wavelength (nm)R

elat

ive

abso

rban

ce(a

.u.)

Entry 1Entry 2Entry 3Entry 4Entry 5

Entry 6Entry 7Entry 8Entry 9Entry 10

400 500 600 700 800

(b)

Figure 3: (a) Representative of normalized XRD data of CuIn0.7Ga0.3S2 nanoparticles prepared at 200◦C. (b) Normalized UV-Vis absorptionspectra of typical CuIn0.7Ga0.3S2 nanoparticles prepared at 200◦C.

Table 2: Composition (from ICP-OES analysis) of soluble CuInxGa1−xS2 nanoparticles prepared at 160, 180, or 200◦C.

Entry Temp. (◦C) Cu% In% Ga% In+Ga In/In+Ga Ga/In+Ga MRW (%)

11 160 18.73 13.00 3.69 16.69 0.78 0.22 34.6

12 180 19.81 12.61 5.95 18.56 0.68 0.32 30.1

13 200 20.48 11.57 7.38 18.94 0.61 0.39 28.4

TGA

DSC

m/z = 27

∗m/z = 60 ∗m/z = 34

m/z = 44

20 mW

50 100 150 200 250 300 350 400 450 500 550◦C

2m

g0.

1n

a

MS

Figure 4: DSC/TGA-MS data for entry 11.

An HRTEM image of CuIn0.61Ga0.39S2 nanoparticles(Table 2, entry 13) is shown in Figure 6. Observed sizesof CuIn0.61Ga0.39S2 nanoparticles are 3.9 nm from HRTEM

images which is consistent with the XRD-calculated size(Figure 5).

In order to demonstrate the reproducibility of the meth-od, we also tried a scale-up version of the previous synthesisfive times on a 5 g scale in 5 different reaction vessels toproduce 25 g of soluble CuIn0.72Ga0.28S2 nanoparticles at onetime.

The analysis of CuInxGa1−xS2 nanoparticles by ICP-OESindicates that our method allows precise control of In andGa ratio. The ICP-OES data of CuIn0.72Ga0.28S2 nanoparticlesalso show evidence of little or no change in the atomicpercent of Cu, In, and Ga for the reactions described inTable 3.

The average bandgap calculated from entries 14 through18 is 1.78 ± 0.05 eV (Figure 7(b)). The estimated volume-weighted crystal diameters [29] of the CuIn0.72Ga0.28S2

chalcopyrite nanoparticles samples are 4.1 ± 0.2 nm(Figure 7(a)).


2θ

Rel

ativ

ein

ten

sity

Entry 11

Entry 12

Entry 13

10 20 30 40 50 60

(a)

Entry 11Entry 12Entry 13

Wavelength (nm)

Rel

ativ

ein

ten

sity

(a.u

.)

560 610 660 710 760

(b)

Figure 5: (a) Normalized XRD data of typical CuInxGa1−xS2 soluble nanoparticles prepared from 160 to 200◦C. (b) Normalized pho-toluminescence spectra of typical CuInxGa1−xS2 soluble nanoparticles prepared from 160 to 200◦C.

Table 3: Composition (from ICP-OES analysis), optical bandgaps (Eg) (from UV-Vis spectra), and sizes (from XRD) of solubleCuIn0.72Ga0.28S2 nanoparticles prepared at 195◦C.

Entry Cu% In% Ga% In+Ga In/In+Ga Ga/In+Ga Eg (eV) Size (nm)

14 21.77 14.85 5.59 20.44 0.73 0.27

1.78 4.115 20.92 14.51 5.42 19.93 0.73 0.27

16 21.47 14.23 5.28 19.50 0.73 0.27

17 20.99 13.53 5.76 19.29 0.70 0.30

18 21.51 15.32 5.36 20.67 0.74 0.26

10 nm

Figure 6: HRTEM image of CuIn0.61Ga0.39S2 nanoparticles at200◦C.

4. Conclusion

The multigram scale synthesis of CIGS alloy nanoparticlesis discussed. Potentially, these nanoparticles can be incor-porated into next-generation quantum dot-based solar cells.

The ability to prepare quaternary CuInxGa1−xS2 (0 ≤x ≤ 1) chalcopyrite nanoparticles with precise controlof stoichiometry is important for controlling the bandgapand, therefore, the absorption behavior of the materials. Thereaction temperatures are also critical for fine control ofnanoparticle sizes and bandgaps. We have shown that byexploiting the microwave-assisted decomposition of two dif-ferent SSPs in the presence of 1,2-ethanedithiol, we efficientlyprepared CuInxGa1−xS2 (0 ≤ x ≤ 1) nanoparticles. Shortreaction times of less than 1 hour have been achieved for thepreparation of these nanoparticles. Two major advantages ofthis approach are precise stoichiometric control of In and Garatio and controlling the size of nanoparticles by reactiontemperatures. A wide range of bandgaps can be engineeredthrough a combination of precise control of elemental com-position and particle sizes. We are currently exploring the useof various related SSPs to prepare multinary nanoparticlesthat exhibit an even wider range of bandgaps and otherunique optoelectric behaviors.


2θ

Rel

ativ

ein

ten

sity

Entry 14

Entry 15

Entry 16

Entry 17

Entry 18

10 20 30 40 50 60

(a)

Entry 14Entry 15Entry 16

Entry 17Entry 18

Wavelength (nm)

Rel

ativ

eab

sorb

ance

(a.u

.)

450 500 550 600 650 700 750 800

(b)

Figure 7: (a) Normalized XRD data of CuIn0.72Ga0.28S2 soluble nanoparticles prepared 195◦C. (b) Normalized UV-Vis absorption spectraof CuIn0.72Ga0.28S2 soluble nanoparticles prepared 195◦C.

Acknowledgments

The authors are thankful for The financial support receivedthrough DOE EPSCoR Grant no. DE-FG02-04ER46142 andsubgrant no. DE-FG02-04ER46142 (PL). A. Punnoose wouldlike to acknowledge The financial support from NSF-MRI0521315 (TEM). J. D. Harris would like to acknowledgeThe financial support from NSF-DMR-0840265 (DSC/TGA-MS).

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